[discoverygo] detect when video needs authentication(closes #10425)

youtube_dl/extractor/discoverygo.py

@@ -7,6 +7,7 @@ from ..utils import (
     int_or_none,
     parse_age_limit,
     unescapeHTML,
+    ExtractorError,
 )
 
 
@@ -53,7 +54,13 @@ class DiscoveryGoIE(InfoExtractor):
 
         title = video['name']
 
-        stream = video['stream']
+        stream = video.get('stream')
+        if not stream:
+            raise ExtractorError(
+                'This video is only available via cable service provider subscription that'
+                ' is not currently supported. You may want to use --cookies.'
+                if video.get('authenticated') is True else 'Unable to find stream',
+                expected=True)
         STREAM_URL_SUFFIX = 'streamUrl'
         formats = []
         for stream_kind in ('', 'hds'):